Time-saving bias

Time-saving bias is a concept that describes people's tendency to misestimate the time that could be saved (or lost) when increasing (or decreasing) speed.

People also underestimate the time that could be lost when decreasing from a low speed and overestimate the time that could be lost when decreasing from a high speed.

In one study, participants were asked to judge which of two road improvement plans would be more efficient in reducing mean journey time.

[4] For example, participants were asked the following question: "You are driving along an open road.

Results supported the predictions of the time-saving bias, as participants underestimated the time saved when increasing from a low speed and overestimated the time saved when increasing from a relatively high speed.

In addition, participants also misestimated the time lost when decreasing speed: they generally underestimated the time lost when decreasing from a low speed and overestimated the time lost when decreasing from a relatively high speed.

Changing the distance of the journey from 10 miles (16 km) to a longer or shorter distance will increase or decrease these time savings, but will not affect the relationship between speed and time savings.

Svenson suggested that people's judgments of time-savings actually follow a Proportion heuristic, by which people judge the time saved as the proportion of the speed increase from the initial speed.

[6] Another study suggested that people might follow a simpler difference heuristic, by which, they judge the time saved based solely on the difference between the initial and higher speed.

[7] It seems that people falsely believe that journey time decreases somewhat linearly as driving speed increases, irrespective of the initial speed, causing the time-saving bias.

Although it is still unclear what is the dominant heuristic people use to estimate time savings, it is evident that almost none follow the above curvilinear relationship.